If you have any concerned with the oil pressure, get it checked with a master gauge, this will give a true indication as to the oil pressure. Now to answer your question, Yes the oil pressure will fluctuate with engine RPM, The oil pump will deliver more oil with higher rpm's so the pressure will increase, but the fact that you can see this change is because there is a loss of pressure to start with, normally through worn bearings, inefficient pump, just a sign that the engine is getting a little on the tired side, but not a real problem, until idle oil pressure drops to a dangerous level hot.